A slit lamp microscope is an ophthalmologic apparatus that uses slit light to cut an optical section of a cornea, thereby obtaining an image of a cross-section of the cornea. As disclosed in Patent Documents 1 and 2, a slit lamp includes a main illumination system for irradiating an eye with slit light and a background illumination system for illuminating an area around the slit light. Light irradiated to an eye by the background illumination system is referred to as background illumination light.
The background illumination system is configured as an optical system that guides light output from a light source in the main illumination system. Therefore, it is difficult to control irradiation of slit light and irradiation of background illumination light independently from each other, and also difficult to link the control of irradiation of slit light with the control of irradiation of background illumination light.